Medical and nursing-care fields have been demanding a safe actuator that is lightweight, flexible, and operable at a low driving voltage adapted for various devices, for example, the electric catheter, the fiber scope, the rehabilitation equipment, the powered suit, the artificial organ and the like. In addition to the above-described advantageous features, the actuator is required to realize a complex motion in a tiny space so as to be adapted for a paper display, a handy tactile device and the like which are expected to be further demanded in future. The actuator is expected to realize not only large stress, quick response, and highly accurate controllability, but also compactness, lightness, flexibility, quietness, and safe portability (low driving voltage type) as a soft actuator in future.
The actuator may be formed of a material that is flexibly deformable in response to an external signal. For example, a piezo actuator using a piezo effect of ferroelectrics, an SMA (shape-memory alloy) actuator using phase transition of the SMA may be well known as the actuator using the deformable material. The piezo actuator exhibits quick response and large stress, but low strain, high driving voltage and less flexibility. Meanwhile the SMA actuator exhibits a high strain, but slow response, low durability, and difficulty in execution of accurate control as the phase transition is performed to strain by changing the temperature through self heating by way of Joule heating. Both types of the actuators may have disadvantages as well as advantages.
Besides the generally employed strain type actuator as described above, the actuator formed of a soft material, that is, a lightweight and soft organic polymer has been employed (hereinafter referred to as an organic actuator). A conducting polymer actuator formed of conducting polymers, for example, polyaniline, polypyrrole and the like as disclosed in JP-A No. 20586/1990, an ionometric polymer-metal composites actuator formed of an ion exchange resin as disclosed in JP-A No. 6991/1994, and a conductive nano-particles composite actuator presented in the technical paper (entitled “Strain type ion conducting polymer actuator”, Ishibashi et al., 53rd annual conference of Society of Polymer Science in 2004, IPA155) may be recognized as the organic actuators. Those actuators are featured by using a lightweight material, having quietness, and being operable at lower driving voltages in the order of several volts, which are soft and safe. The conducting polymer actuator and the conductive nano-particles composite actuator are of strain type like the natural muscle, which exhibit larger stress compared therewith. The conductive nano-particles composite actuator further exhibits excellent durability.
The organic actuator such as the conductive nano-particles composite actuator is basically structured to make a flexible motion upon a voltage input to a counter electrode provided only in an electrolyte solution. If the organic actuator is used in an environment other than the electrolyte solution, a motion made by an organic actuator film operable in the electrolyte solution has to be taken out of the electrolyte solution through the appropriate process.